Various priority systems have been employed for honoring priority requests from a number of different components or elements of a data processing, or information transmitting, system. These priority schemes vary from those in which certain components will always have a higher priority than others, to systems in which the requesting elements are to be provided with equal access time. An example of an ordered priority requesting system is shown in Henzel, et al., U.S. Pat. No. 3,832,692. An example of a pre-emptive rotational priority system is shown in the Danilenko, et al. U.S. Pat. No. 4,009,470.
The present invention is directed to a novel priority system in which the priority scheme may be modified merely by exchanging a programmable read only memory (PROM) with one that is programmed differently. By replacement of the PROM a different number of channels may also be implemented. The network of the present invention may also be added to systems with a nested priority structure.
The priority implementation techniques employed in the prior art require dedicated circuitry in order to implement a particular set priority scheme. In order to obtain a different type of priority scheme, the entire structure would have to be redesigned. With the present invention a particular priority scheme may be replaced with a different scheme merely by replacement of the PROM; or, if desired, different channels of the system may be operated under different priority schemes by dividing the PROM into different sections, each section of which may control a different number of components, such as I/O channels or memory banks.